1. Field of the Invention
The present invention relates to a liquid crystal display, a drive method therefor, and a projection type display apparatus, and in particular, relates to a liquid crystal display suitable for use in a liquid crystal light valve mounted in a projection type display apparatus, and to a drive method therefor.
2. Description of Related Art
As a light modulation device mounted in a projection type display apparatus such as a liquid crystal projector, a liquid crystal light valve is known. The liquid crystal light valve is essentially constructed as a pair of substrates arranged facing each other with a liquid crystal layer therebetween, and is furnished with electrodes for applying a voltage to the liquid crystal layer. Normally, a liquid crystal cell of an active matrix type is used for the liquid crystal light valve, and higher resolution for the image is achieved.
In the drive method for a liquid crystal light valve, in order to prevent burnout or deterioration of the liquid crystal, an inversion drive method, such as dot inversion, line inversion, and surface inversion, has heretofore been adopted. There are both advantages and disadvantages for these inversion drive methods; however, in the case of dot inversion or line inversion, while there is an advantage in being able to control cross-talk, since a potential having an inverted polarity is written to each of adjacent pixel electrodes, a transverse electric field is generated between the adjacent pixels, and there is therefore the likelihood of light passing through caused by disclination due to this transverse electric field. As described above, due to the circumstances in which high resolution is demanded for the liquid crystal light valve, the light passing described above causes a drop in contrast or reduction in opening ratio, becoming a signification factor in reducing display quality. Therefore, from this viewpoint, there is a need to adopt the surface inversion drive method in which transverse electric fields do not occur.
However, in the surface inversion drive method, there are other problems.
That is to say, in the surface inversion drive method, in the case of observing one data line, then with respect to all of the pixels to which signals are supplied from the aforementioned data line, if the inversion period is set to one field, then an image signal (potential) of the same polarity is written in one predetermined field. Then, at the moment of shifting to the next field, the polarity of the image signal supplied to this data line is inverted. At this time, in the case where the scanning lines are scanned from the upper stage side to the lower stage side of the display area, there is the condition where at the pixels on the upper stage side of the display area, after the image signal is written, then in the time of approximately the hold period, the polarity of the image signal applied to the relevant data line is the same polarity as the potential of the pixel, while in contrast to this, at the pixels on the lower stage side, after the image signal is written, then in the time of approximately the hold period, an image signal of the polarity inverted to that of the pixel is applied to the data line. In this manner, at the upper stage side and lower stage side of the display area, a difference occurs in the influence that the potential of the data line provides on the pixel electrode. For this reason, there is a problem in that the display becomes non-uniform depending on the location on the screen.
Therefore, as a device which can suppress cross-talk, and which can secure uniformity of the screen, there has been proposed a technique where one horizontal period is divided into a first period and a second period, and in the first period, a driving pulse is supplied to a scanning line, and at the same time, an image signal is supplied to a data line to thereby apply an image signal to each pixel electrode, while on the other hand, in the second period, an image signal having the polarity inverted to the previous polarity is supplied to the data line without supplying a driving pulse to the scanning line, for example, in Japanese Unexamined Patent Application, First Publication No. Hei 5-313608.
However, in the technique disclosed in the above-mentioned patent document, the time which can be used in writing to the pixel is half the normal time, so that problems such as insufficient writing occur.